1. Field of the Invention
This invention relates to an air bearing type machine tool to support a main shaft by an air bearing, which is for carrying out a cutting process of various materials, such as steel, iron, non-ferrous metal, wood, stone, glass, graphite, plastic, ceramic and so on.
2. Description of the Related Art
In a typical machine tool for carrying out a cutting process or the like, a main shaft attached thereto with a tool is generally supported by an antifriction bearing. In some machine tools, an oil bearing of dynamic pressure or static pressure is used as a bearing for the main shaft.
Further, lately, there has been an ultra-precise machine using a static air bearing having extremely low-friction as the bearing for the main shaft.
However, the aforementioned conventional bearings have the following disadvantages.
More specifically, when the antifriction bearing is used as the bearing for the main shaft, the product of the rotational number and the diameter of orbit of which a rolling element is rotated is limited to a fixed threshold value dependent upon a structure of the bearing or the like, so that there is a disadvantage that it is difficult to rotate the main shaft at high-speeds. Therefore, the rotational speed of the main shaft is slower, resulting in a disadvantage that it is difficult to shorten the processing time.
Incidentally, lately, the structure of the bearing has been developed to pave the road to rotate the main shaft at high speeds by various inventions even when the antifriction bearing is used, but there are disadvantages that a vibration and noise are large and the life of the main shaft or the bearing is shorter. Especially, the short life causes the need for a routine replacement of the main shaft or the bearing in order to maintain production, resulting in a disadvantage of the extremely great cost of processing including replacement costs in the great-efficient high-speed process to rotate the main shaft at high speeds.
The antifriction bearing cannot basically avoid producing a vibration by microscopic asperities on the transferring face or a sphericity error of each rolling element, resulting in a basic disadvantage that it is difficult to improve the processing accuracy and to carry out the process in high speeds.
In the oil bearing of the dynamic pressure or the static pressure, when the main shaft is rotated at high speed, the sharing resistance of oil is increased, resulting in an uneconomical disadvantage caused by increasing power consumption.
Heat, caused by increasing power consumption produces, thermal deformation of the main shaft or the bearing, resulting in a disadvantage of reduction of the processing accuracy.
In the conventional static air bearing, a supplied air pressure is approximate 5 atmospheric pressure to 7 atmospheric pressure, the rigidity of the bearing is insufficient for processing iron, steel or the like which needs high load, therefore the bearing cannot be used except for precisely processing for soft metal, such as bronze, aluminium, silicone or the like.
The applicants have been developed a machine tool capable of processing for iron, steel or the like which needs high load by improving the rigidity of the bearing by increasing the pressure of air supplied to the static air bearing, but newly found an uneconomical disadvantage of using high amounts of energy because an amount of air used is increased as the air pressure is increased.
It is an object of the present invention to provide the air bearing type machine tool capable of processing for cutting iron or steel or the like which needs high load, and saving energy by controlling an amount of air used.